Secondary Thermohydraulic Quench Detection for the ITER Correction Coils

The primary quench detection for ITER magnets is classically based on resistive voltage measurements. In addition, a safety related secondary quench detection relying on signals of thermohydraulic nature is required for the TF coils. Although not required by safety, a similar secondary quench detection system has been investigated for the other ITER coils [central solenoid (CS), poloidal field (PF), and correction coil (CC)]. The quenches in the ITER bottom correction coil (BCC3) of either the top pancake (P8) or the whole coil (eight pancakes), without a current fast discharge, are studied using the coupled Gandalf and Flower codes. The minimum quench energy is deposited in the area where the temperature margin is minimal, close to the outlet of the conductor. Because PF5, BCC3, and BCC6 are hydraulically linked in parallel, the influence of a PF5 coil quench without a fast discharge is studied. For all these cases, the cryogenic consequences are determined providing qualitative and quantitative information. Key signals are presented like pressure, temperature, and mass flows in the conductor itself, as well as at the ends of feeders, in the Cold Termination Box, where the sensors are located. The feasibility of the secondary thermohydraulic quench detection is investigated, leading to an associated proposal for the instrumentation (difference of mass flows: inlet-outlet). The main conclusions concerning these signals are discussed.